Search Results (8 total)

Dynamics of interaction of longitudinal modes in a FEM oscillator with a broad-frequency-band feedback system and a klystronlike interaction region is studied. It is shown that the use of the klystronlike interaction region results both in increasing the efficiency of electron energy extraction and decreasing the number of competing modes. The latter provides a significant increase of the electron-current threshold of stability of the single-mode operation.

A method of organizing electron-wave interaction at the multiplied frequency of the signal wave is proposed. This type of electron-wave interaction provides multiplied-frequency electron bunching, which leads to formation of an intense harmonic of the electron current at a selected multiplied frequency of the signal wave. This effect is attractive for the use in klystron-type cyclotron masers with frequency multiplication as a way to increase the output frequency and improve the selectivity.

The effect of “pressing out” of a short rf powerful pulse by an electron beam from a Bragg cavity pumped by a low-power input rf signal is studied. This effect occurs as a result of the transient process from the “cold” (without the electron beam) steady state of the system to the “hot” one. It is shown that the peak power of the output pulse can be significantly higher than both the pumping rf power and the electron beam power. As for the duration of the output pulse, it is fixed by the cold characteristics of the microwave system.

A spatially modulated (corrugated) electron beam provides Bragg-type scattering of two waveguide modes. This allows the use of corrugated beams as quick active elements in rf-pulse compressors. In an illustrative example shown with a peak power compression ratio of 20-40, a 10–20 ns output pulse with a peak power of tens of MW is predicted for a millimeter-wavelength compressor.

A different version of the regime of electron trapping is proposed for electron microwave amplifiers. The use of this regime in a cyclotron resonance maser with a weakly relativistic electron beam can simultaneously provide efficiency as high as 50%, a very broad (tens of percent) frequency band, and very weak sensitivity to the spread in electron velocity.

A novel type of the frequency-tunable oscillator based on simultaneous generation of the forward and opposite waves at the same frequency, but at different cyclotron harmonics, is proposed. A spatially periodic helical electron beam allows for strong coupling of the waves. The opposite wave provides the broadband feedback and electron bunching, whereas the forward wave amplifies the arising signal and withdraws the rf power from the interaction region. A 15% efficiency and 5% frequency bandwidth have been achieved in the first experiment.

For a cyclotron resonance maser (CRM) with a helical axis-encircling electron beam, the possibility of a strong interaction between cutoff (gyrotron) and traveling Doppler-up-shifted (cyclotron autoresonance maser) modes, which are in resonance with the electrons at the same frequency, is demonstrated. This effect can be used in a CRM oscillator of a new type, where the feedback and the mode selectivity for the operating traveling mode are provided due to the excitation of the cutoff mode. According to both the theory and the experiment, such a scheme can provide an effective excitation of the traveling mode with negligibly low losses associated with the cutoff mode.

A high-power, frequency-tunable electrostatic free-electron maser, being developed at the FOM Institute for Plasma Physics “Rijnhuizen,” shows lasing at various frequencies. An output power of 730 kW at 206 GHz is generated by a 7.2-A, 1.77-MeV electron beam, and 380 kW at 165 GHz is generated by a 7.4-A, 1.65-MeV electron beam. In the present experimental setup, without recovery of the spent electron beam power, the pulse length is limited to 12 μs. Nevertheless, the main issues, such as the possibility of high-power, single-mode operation and frequency tuning, have been confirmed. The experimental results and the dynamics of the laser process are well in accordance with simulations.